The study of the concept of electrophilic chemical carcinogenesis will be continued on the following significant pro-carcinogens. 1) Polycylic aromatic hydrocarbons 2) Aromatic amines and nitro compounds 3) Nitrosoamines and related compounds. The nature of the active electrophilic agents will be determined under conditions allowing observations of stable long-lived carbocationic intermediates with methods previously developed in our laboratories, i.e., 1H, 13C NMR ESCA (photoelectron) spectroscopy. The alkylating ability of carbocationic electrophiles formed by chemical activation of pro-carcinogens will also be studied.